US 20050265485 A1
A multiplexing scheme to select either an I component or a Q component for input to I channel and Q channel inputs of a baseband receiver. The selection of which of the I or Q component to place on the I channel input and which other to place on the Q channel input is based on, there being a correct relationship of the I and Q components received from a RF processing stage of a wireless communication device or if the I and Q components have incorrect relationship because they are interchanged.
1. An apparatus comprising:
a receiver to receive converted radio frequency (RF) signals having an in-phase component I and a quadrature component Q to recover data from a demodulated signal; and
a switching circuit to select between two converted RF signals that are out of phase with one another, in which an in-phase signal is to be selected as the component I for I channel input to the receiver and an out-of-phase signal is to be selected as the component Q for Q channel input to the receiver.
2. The apparatus of
3. The apparatus of
4. The apparatus of
5. The apparatus of
6. An integrated circuit comprising:
an analog-to-digital converter (ADC) to couple to a radio frequency (RF) processor to receive converted analog signals from the RF processor, the converted analog signals having an in-phase component I and a quadrature component Q, and to convert the analog I and Q components to digital I and Q components;
a switching circuit coupled to the ADC to select between the digital I and Q components to have the digital I component for input into an I channel input of a baseband receiver and to have the digital Q component for input into a Q channel input of the baseband receiver when the I and Q components are in correct phase relationship on a signal constellation map, but to select the digital Q component for input into the I channel input of the baseband receiver and digital I component for input into the Q channel input of the baseband receiver when the I and Q components are interchanged relative to their correct relationship.
7. The integrated circuit of
8. The integrated circuit of
9. The integrated circuit of
10. The integrated circuit of
11. The integrated circuit of
12. A method comprising:
receiving an in-phase component I and a quadrature component Q as converted RF signals;
selecting the in-phase component for input into an I channel input and quadrature component for input into a Q channel input to obtain a demodulated signal, if the in-phase and quadrature components are in correct phase relationship on a signal constellation map; and
selecting the in-phase component for input into the Q channel input and quadrature component for input into the I channel input to recover data from a demodulated signal, if the in-phase and quadrature components are interchanged relative to their correct relationship.
13. The method of
14. The method of
15. The method of
16. A method comprising:
receiving a radio frequency (RF) signal in a wireless transmission;
converting the RF signal to generate an in-phase component I and a quadrature component Q in analog format;
converting the I and Q components to digital format;
selecting the in-phase component for input into an I channel input and quadrature component for input into a Q channel input to recover data from a demodulated signal, if the in-phase and quadrature components are in correct phase relationship on a signal constellation map;
selecting the in-phase component for input into the Q channel input and quadrature component for input into the I channel input to obtain a demodulated signal, if the in-phase and quadrature components are interchanged relative to their correct relationship; and
recovering data at a baseband frequency.
17. The method of
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1. Technical Field of the Invention
The embodiments of the invention relate to wireless communication systems and, more particularly, to integrated circuits used in such wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Generally, each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, etc., communicates directly or indirectly with other wireless communication device(s). For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For a wireless communication device to participate in wireless communications, it generally includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter may include a data modulation stage, one or more intermediate frequency (IF) stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillator signal(s) to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and may include a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies the signal. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillator signal(s) to convert the amplified RF signal into baseband signals or IF signals. The filtering stage filters the baseband or IF signals to attenuate frequencies outside of the bandwidth of the filter to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard employed.
In some signal processing techniques employed for wireless communications (e.g., differential phase shift keying (DPSK) or quadrature phase shift keying (QPSK)) a signal may be depicted using a two-dimensional constellation diagram, where the number of points on the constellation graphically represents the complex envelope of possible symbol states. The x-axis of a constellation diagram represents the in-phase (I) component of the complex modulation envelope and the y-axis represents the quadrature (Q) component of the complex modulation envelope. Generally, when signals are transmitted based on a certain constellation pattern, the transmitted intelligence may be recovered if the receiving unit is able to demodulate based on the same constellation pattern.
However, if for any reason the I and Q components are interchanged, causing the I and Q axes to flip, then in that instance the recovered data is unintelligible. Accordingly, a need exists for a technique to compensate for the I and Q axes, if a condition occurs that may cause the two axes to flip.
An apparatus and method to select in-phase and quadrature components for I and Q channel inputs of a baseband processor. In order to demodulate and recover data correctly, a converted RF signal is coupled to a baseband receiver with I and Q components. A switching circuit is utilized to switch the I and Q components onto corresponding I and Q channel inputs if the I and Q components are in correct phase. However, if the I and Q components are for some reason interchanged, then the Q component is utilized for the I channel input of the baseband receiver and the I component is utilized for the Q channel input of the baseband receiver.
In one embodiment, multiplexers are used as the switching circuit. The multiplexers may be made programmable so that the selection of inputs to the I and Q channels may be programmably controlled. In one embodiment, the programming control for the multiplexers is achieved by a value stored in a register.
Although embodiments of the invention may be applicable in various devices, one example is the implementation of the invention in a wireless communication system, in which the multiplexers reside in an integrated circuit chip that includes a baseband receiver.
The embodiments of the present invention may be practiced in a variety of settings that implement conversion of a RF signal to recover intelligence.
The base stations or access points (BS/AP) 11-13 may be operably coupled to network hardware 14 via respective local area network connections 15-17. Network hardware 14, which may be a router, switch, bridge, modem, system controller, etc., may provide a wide area network connection 18 for communication system 10. Individual BS/AP 11-13 generally has an associated antenna or antenna array to communicate with the various wireless communication devices in its area. Typically, the wireless communication devices register with a particular BS/AP 11-13 to receive services within communication system 10. For direct connections (i.e., point-to-point communications), wireless communication devices may communicate directly via an allocated channel.
Typically, base stations are used for cellular telephone systems and like-type systems, while access points are used for in-home or in-building wireless networks. Regardless of the particular type of communication system, an individual wireless communication device includes a built-in radio and/or is coupled to a radio. The radio may include a linear amplifier and/or programmable multi-stage amplifier to enhance performance, reduce costs, reduce size, and/or enhance broadband applications. It is to be noted that an embodiment of the invention may be implemented in one or more of the various units 11-13 and/or 20-27 of
As shown in the embodiment of
In the example device 30, digital front end 31 includes a host processor 35, media access control (MAC) unit 36, interface 37 and one or more input/output (I/O) connections. In the particular example device 30, Peripheral Component Interconnect (PCI) connection 38 and Personal Computer Memory Card International Association (PCMCIA) connection 39 are shown as just two examples of the I/O interfaces available. It is to be noted that other connection and bus standards may be used to provide coupling to the interface 37.
MAC unit 36 generally provides the node address(es) for various nodes on the network, if device 30 is coupled onto a network. A host processor 35 may be present to control the operation of digital front end 31 and/or to process incoming and/or out-going data, if such data processing is needed prior to inputting data to baseband processor 32 and/or outputting data to the user. Therefore, in a typical operation, data input from a user is received by digital front end 31 and sent to baseband processor 32 when data is ready to be transmitted. Similarly, when data is received by wireless communication, the digital data output from baseband processor 32 is coupled to digital front end 31 to be made available for use by the user. It is to be noted that other embodiments for the digital front end may include additional components, such as memory, processing modules or other interfaces. Furthermore, digital front end 31 may be part of a stand alone device, so that coupling to a network may not be needed. In other instances, the digital front end may perform corresponding communication functions in accordance with a particular standard, such as a cellular telephone standard.
Baseband processor 32 includes a transmitting (Tx) module 40 to receive digital data from digital front end 31 and process the digital data for conversion as outbound signals to RF processor 33. Likewise, baseband processor 32 also includes a receiving (Rx) module 42 to receive inbound signals from RF processor 33 and convert the inbound signals as digital data for output to digital front end 31. In the particular embodiment shown for baseband processor 32, Tx module 40 resides in the transmitting path and converts the digital signal from digital front end 31 to an in-phase component I and quadrature component Q pursuant to a known digital modulation technique. The outbound I and Q components are then coupled to a digital-to-analog converter (DAC) 41 to convert the digital component signals into analog signals. The Q and I analog components are then coupled to RF processor 33 as modulation signals. It is to be noted that DAC 41 may be comprised of one or more DAC units to provide the digital-to-analog conversion.
On the receiving path, the inbound RF signals are converted into Q′ and I′ components in RF processor 33 and coupled to an analog-to-digital converter (ADC) 43 for conversion to digital signals as part of demodulation. ADC 43 may be comprised of one or more ADC units to provide the analog-to-digital conversion. The digital Q′ and I′ components are then coupled to Rx module 42 through a multiplexer (MUX) 44. As will be described below, a function of MUX 44 is to select which one of the I′ or Q′ component to be used for the in-phase component I channel input to Rx module 42 and which other Q′ or I′ component to be used for the quadrature component Q channel input to Rx module 42. Although a multiplexer is shown, it is to be noted that other switching devices may be utilized for the Q′ and I′ selection input to Rx module 42. Rx module 42 receives the Q and I digital components and combines the components to generate a digital signal for output to the digital front end 31.
It is to be noted that a variety of circuitry may be utilized for Tx and Rx modules to perform the Q and I component conversions, including circuitry known in the art. Furthermore, although not shown, other components may be resident in baseband processor 32, such as memory. What is to be noted is that the Tx module receives digital data from the digital front end and Q and I components are generated from the performed conversion in the Tx module. Likewise, in the receiving path, the Rx module receives the Q and I components and performs the conversion to generate a digital data output to the digital front end.
RF processor 33 includes a radio core 50 for transmitting and receiving modulated RF signals. Radio core 50 receives the analog signal from baseband processor 32 and after filtering, uses the analog signal to modulate a signal envelope at a higher frequency, generally referred to as RF. A variety of modulation techniques may be employed, including modulation techniques known in the art. The baseband frequency may be converted directly to RF or one or more intermediate frequency (IF) conversion stage(s) may be employed. A typical technique is to employ a local oscillator and a mixer to perform the up-conversion operation to generate a modulated RF envelope. The RF signal is typically amplified and transmitted from an antenna 55.
Radio core 50 also receives RF signals through antenna 55 and employs a technique in reverse to demodulate a baseband signal from the received RF signal. Again, one or more IF conversion stages may be employed with a local oscillator, if direct conversion from RF to baseband frequency is not used. A low noise amplifier may be employed to amplify the received RF signal prior to demodulation. A variety of conversion techniques may be employed, including conversion techniques known in the art. The baseband components are then output to baseband processor 32.
It is to be noted that various other components may be employed within radio core 50 to perform functions for modulation and demodulation. These components may include memory components, various filters (such as low-pass filters), low noise amplifiers to increase the gain of the received signal, power amplifiers to boost the power of the transmitted signal, local oscillators and mixers to perform the frequency conversion, as well as a switching controller at the antenna to switch between transmit and receive modes. Generally, a single antenna may be utilized. However, in other embodiments, separate antennae may be used for transmitting and receiving.
It is also to be noted that Tx and Rx units 40, 42 of baseband processor 32 may also perform one or more operations including, constellation mapping/demapping, encoding/decoding, scrambling/unscrambling, as well as further frequency conversion. Generally, a particular wireless communication standard (e.g., IEEE 802.11 Bluetooth, etc.) is employed by the Tx and Rx units. The Tx and Rx units may be separate units or may employ shared units.
Furthermore, it is to be noted that device 30 of
Subsequently, signal WI(t) is mixed with a local oscillator signal LoI to generate WI(t) Cos (2πfct). The signal WQ(t) is mixed with a local oscillator signal LoQ, which has a 90 degree phase shift from LoI, to generate WQ(t) Sin (2πfct). The summation of the two modulated signals produce an RF output X(t) at antenna 61, where X(t)=WI(t) Cos (2πfct)−WQ(t) Sin (2πfct). When using various coded standards, such as for example, differential phase shift keying (DPSK) or quadrature phase shift keying (QPSK), the intelligence is carried in the sideband(s) and not in the carrier (fc).
The transmitted RF is received by a wireless receiver unit 70. The signal X(t) is received at antenna 71 and coupled to a receiver section of an RF processor 73. In one embodiment, RF processor 73 is equivalent to RF processor 33 of
The converted analog signals are then coupled to baseband processor 72. In one embodiment, baseband processor 72 is equivalent to baseband processor 32 of
Typically, for proper operation of baseband processor 72, baseband processor 72 expects the YI(t) component to be the in-phase component I. That is, YI(t) component is expected to be X(t) Cos (2πfct) when converted in RF processor 73 and output to ADC 80. Likewise, YQ(t) component is expected to be X(t) Sin (2πfct) when converted in RF processor 72 and output to ADC 81. There is a 90 degree phase difference between the two components, due to the operation of the LoQ. However, in some instances, the expected Q′ and I′ components from RF processor 73 may not be in correct phase relationship for input into respective Q and I channels of the receiver.
In order to adjust for the situation when an unwanted exchange of the I′ and Q′ components occurs, an embodiment of the invention shown in FIGS. 3 uses MUXs to select the appropriate outputs to the I and Q channels of the receiver. In
It is to be noted that the MUXs 83, 84 correspond to the MUX 44 of
Although a variety of MUX switching control techniques may be utilized, in the embodiment of
As one example, if the RF processor 73 and baseband processor 72 are separate IC chips, it is possible that a situation may occur where RF processor 73 may be replaced with another. Such a condition may occur if an enhanced RF IC chip is available for replacing an older chip on a board. If the circuit characteristics of the new RF processor unit reverses the interpretation of the I and Q components, then the baseband unit can readily adjust for the new RF IC by programming register 85 to select the Q′ output for the I channel and I′ output for the Q channel. Without this selectability, significant circuit adjustment may be needed or even the replacement of the baseband unit itself. Thus, MUX 83, 84 allow flexibility in adjusting for circuit changes in the design of wireless device 70 by selecting appropriate signals for the I and Q channels. In one embodiment, this flexibility is made programmable.